In the past, the alkylation of aromatic hydrocarbons with non-heteroatom-containing hydrocarbons was achieved by one of two methods. The first method comprises the reaction of an aromatic hydrocarbon with an olefin such as ethylene or propylene.
Alkylation of aromatic hydrocarbons with an olefin in the presence of a crystalline metallic aluminosilicate having uniform large pore openings of about 6 to 15 Angstrom units is described in U.S. Pat. No. 2,290,607 (Lavaud). U.S. Pat. No. 3,251,897 (Wise) describes alkylation of aromatic hydrocarbons in the presence of X- or Y-type crystalline aluminosilicate zeolites, specifically such large pore zeolites wherein the cation is rare earth and/or hydrogen. U.S. Pat. Nos. 3,751,504 (Keown, et al.) and 3,751,506 (Burress) describe vapor phase alkylation of aromatic hydrocarbons with olefins, e.g. benzene with ethylene, in the presence of a ZSM-5 type medium pore zeolite catalyst. U.S. Pat. No. 3,755,483 (Burress) describes alkylation of aromatic hydrocarbons with olefins in the presence of a crystalline aluminosilicate zeolite material. U.S. Pat. Nos. 4,086,287 (Kaeding, et al.) and 4,117,024 (Kaeding) describe alkylation of monoalkyl benzenes with ethylene in the presence of a crystalline aluminosilicate zeolite material. U.S. Pat. No. 4,375,573 (Young) describes alkylation of mono-substituted aromatic compounds with olefins in the presence of a crystalline aluminosilicate zeolite material.
U.S. Pat. No. 4,524,230 (Haensel) describes a process for preparing alkylaromatic compounds by alkylating an aromatic material with paraffinic hydrocarbons; such as ethane, propane, n-butane, iso-butane, etc., over a catalyst having no acid activity. The paraffin material is catalytically decomposed in the presence of the nonacid-acting catalyst to give an olefin fragment which is "scavenged" by the aromatic material. The catalyst is at least one metal of Group VIII of the Periodic Table on a non-acidic solid support.
In a second method, alkylaromatic compounds are prepared by utilizing paraffinic hydrocarbons as indirect alkylating agents. U.S. Pat. Nos. 4,085,156 (Frilette, et al.) and 4,157,950 (Frilette, et al.) describe alkylation of aromatic hydrocarbons with materials derived from paraffins or cycloparaffins over a crystalline aluminosilicate zeolite characterized by a silica-to-alumina ratio of at least 10. These paraffins consist essentially of C.sub.6.sup.+ hydrocarbon which can contain significant amounts of pentane, but C.sub.2 -C.sub.4 hydrocarbons are not present in significant amounts.
In these methods, the reactive alkylating species is usually an olefinic material, either added as part of the feed or, as in the Frilette method, generated in situ from paraffins by cracking. The cracking of the paraffin produces an olefin and a paraffin fragment of which only the olefinic fragment is effective for alkylating the aromatic compound, so that alkylation selectivity is limited to a maximum of 50 percent.